Water supply tube for steam generator

ABSTRACT

The water supply tube for steam generator includes an insert tube portion inserted in a penetration hole of a shell member and a generator internal tube portion connected to the insert tube portion. The generator internal tube portion includes a tubular passage and an effluence tube allowing effluence of cooling water in the tubular passage to a space in a steam generator. The tubular passage includes a first tilted portion in which a side having a greater distance from the insert tube portion along a flow direction is located vertically higher than a side having a smaller distance from the insert tube portion and a second tilted portion which is located with a greater distance from the insert tube portion than the first tilted portion.

FIELD

The present invention relates to a water supply tube for a steamgenerator.

BACKGROUND

Conventionally, a water supply tube for supplying cooling water into asteam generator of a pressurized water reactor or the like is known.When steam or high-temperature water in a generator flows into a watersupply tube or such similar state happens, thermal stratification mayoccur in the water supply tube. Thermal stratification might generatestress causing fatigue and therefore is not preferable.

In Patent Literature 1, a technique applied to a water supply tube for asteam generator is disclosed, in which a dam is attached to an innerupper wall of the water supply tube bent to raise a water supply ring.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Utility Model Laid-open No. 61-121304

SUMMARY Technical Problem

Further consideration can be made to prevent thermal stratification in awater supply tube. The object of the present invention is to provide awater supply tube for a steam generator capable of suppressing thermalstratification in the tube.

Solution to Problem

According to an aspect of the present invention, a water supply tube fora steam generator includes: an insert tube portion horizontallyextending and configured to be inserted in a penetration holepenetrating a shell member of the steam generator; and a generatorinternal tube portion connected to the insert tube portion and arrangedinside the steam generator. The generator internal tube portion includesa tubular passage formed in an axial direction of the generator internaltube portion and an effluence unit allowing effluence of cooling waterin the tubular passage from the tubular passage to a space in the steamgenerator, the tubular passage allowing cooling water supplied fromoutside the steam generator via the insert tube portion to flow in thetubular passage. The tubular passage includes a first tilted portionwhich is tilted so that a side having a greater distance from the inserttube portion along a flow direction of cooling water is locatedvertically higher than a side having a smaller distance from the inserttube portion and a second tilted portion which is located with a greaterdistance from the insert tube portion along the flow direction than thefirst tilted portion and is tilted so that a side having a greaterdistance from the insert tube portion along the flow direction islocated vertically lower than a side having a smaller distance from theinsert tube portion. In at least a portion of a section, along the flowdirection, of the tubular passage between the first tilted portion andthe second tilted portion, a bottom end of a cross section,perpendicular to the flow direction, of the tubular passage is arrangedvertically higher than a horizontal plane including a top end of aninner wall surface of the insert tube portion at a connection betweenthe insert tube portion and the generator internal tube portion.

According to the water supply tube for a steam generator, thermalstratification caused by a steam-pocket generated in an insert tubeportion can be suppressed by suppressing the decrease in water level inthe insert tube portion. Further, in a case when the cooling waterhaving different temperature from the cooling water in the insert tubeportion flows in, the effluence of the cooling water having hightemperature to the generator internal tube portion is generated tosuppress the thermal stratification.

Advantageously, in the water supply tube for a steam generator, theeffluence unit is not included in a section, of the generator internaltube portion, in which the first tilted portion is formed.

According to the water supply tube for a steam generator, the decreasein water level in the insert tube portion can be suppressed even whenthe cooling water level in the steam generator decreases.

Advantageously, in the water supply tube for a steam generator, thegenerator internal tube portion includes a ring tube portion extendingin a ring shape along an inner circumferential surface of the shellmember and a connection tube portion branching off from the ring tubeportion to connect the ring tube portion and the insert tube portion.The first tilted portion is provided as the tubular passage formed inthe connection tube portion, and the second tilted portion is providedas the tubular passage formed in the ring tube portion, the secondtilted portion being formed on each of both ends, in an axial direction,of the ring tube portion with the connection tube portion in between.

According to the water supply tube for a steam generator, a first tiltedportion and a second tilted portion can be formed by suppressinginterference against other structures in the steam generator.

Advantageously, in the water supply tube for a steam generator, ahorizontal ring tubular passage which is the tubular passage extendingin a horizontal direction is formed in a portion, arranged farther thanthe second tilted portion from the insert tube portion along the flowdirection, of the ring tube portion, and a top end of a cross section,perpendicular to the flow direction, of the horizontal ring tubularpassage is provided vertically lower than the horizontal plane includingthe top end of the inner wall surface of the insert tube portion at theconnection between the insert tube portion and the generator internaltube portion.

According to the water supply tube for a steam generator, when thecooling water level in the steam generator decreases, generation of asteam-pocket in a horizontal ring tubular passage is suppressed sinceexposure of a ring tube portion is suppressed.

Advantageously, in the water supply tube for a steam generator, ahorizontal ring tubular passage which is the tubular passage extendingin a horizontal direction is formed in a portion, arranged farther thanthe second tilted portion from the insert tube portion along the flowdirection, of the ring tube portion, and a top end of a cross section,perpendicular to the flow direction, of the horizontal ring tubularpassage is arranged vertically lower than a lower limit of a target forcontrolling a water level of cooling water in the space in the steamgenerator.

According to the water supply tube for a steam generator, even when thecooling water level in the steam generator decreases to a lower limit ofthe target for controlling the water level, generation of a steam-pocketin the horizontal ring tubular passage is suppressed.

Advantageous Effects of Invention

According to the present invention, the thermal stratification in awater supply tube for a steam generator can be suppressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a steam generator according to anembodiment.

FIG. 2 is a cross sectional view of the water supply tube for a steamgenerator according to the embodiment.

FIG. 3 is a perspective view illustrating the water supply tube for asteam generator according to the embodiment.

FIG. 4 is a perspective view illustrating an essential portion of thewater supply tube for a steam generator according to the embodiment.

FIG. 5 is a cross sectional view illustrating an example of the watersupply tube capable of suppressing thermal stratification in an inserttube portion.

FIG. 6 is a perspective view illustrating an example of the water supplytube capable of suppressing thermal stratification in the insert tubeportion.

DESCRIPTION OF EMBODIMENTS

A water supply tube for a steam generator according to an embodiment ofthe present invention will be described below in detail referring to thedrawings. The present invention is not limited to the embodiment. Thecomponent of the embodiment described below includes such componentwhich can easily be conceived by those skilled in the art, or componentssubstantially the same.

Embodiment

The embodiment will be described referring to FIG. 1 to FIG. 6. Theembodiment relates to a water supply tube for a steam generator. FIG. 1is a schematic view of a steam generator according to the embodiment.FIG. 2 is a cross sectional view of a water supply tube for a steamgenerator according to the embodiment. FIG. 3 is a perspective viewillustrating the water supply tube for a steam generator according tothe embodiment. FIG. 4 is a perspective view illustrating an essentialportion of the water supply tube for a steam generator according to theembodiment. Note that, FIG. 2 illustrates a cross section of the watersupply tube for a steam generator viewed along the horizontal directionas shown in the arrow I in FIG. 3.

The steam generator 1 is used for, for example, the PWR (PressurizedWater Reactor). Light water is used as a nuclear reactor coolant and aneutron moderator in the pressurized water reactor. In the pressurizedwater reactor, light water with high temperature and high pressure,which does not boil throughout the reactor internal, is supplied to thesteam generator 1 as primary cooling water. The steam generator 1transfers the heat of the high-temperature and high-pressure primarycooling water to secondary cooling water to generate steam in thesecondary cooling water. With this steam, a turbine generator is rotatedto produce power.

The steam generator 1 extends in the up-and-down direction to form asealed hollow cylindrical shape. The steam generator 1 includes a bodyportion 2 having an upper half portion and a lower half portion of whichdiameter is slightly smaller than that of the upper half portion. Thebody portion 2 is a shell member of the steam generator 1. In the lowerhalf portion of the body portion 2, a tube bundle shroud 3 formed in acylindrical shape is provided so as to be arranged with a predeterminedgap against the inner wall surface of the body portion 2. The tubebundle shroud 3 extends downward so that the bottom end portion of thetube bundle shroud 3 is located just above the tube plate 4 arranged inthe lower part of the lower half portion of the body portion 2. A heatexchange tube bundle 51 composed of a plurality of heat exchange tubes 5each formed in an inverted U-shape is provided in the tube bundle shroud3. Each heat exchanger tube 5 is arranged so as the U-shaped arc portionto be in the upper side. The end portion in the bottom side of each heatexchanger tube 5 is supported by the tube plate 4 and the middle portionof each heat exchanger tube 5 is supported by a plurality of tubesupporting plates 6. In the tube supporting plate 6, a large number ofpenetration holes (not shown in the drawing), in each of which the heatexchanger tube 5 is inserted to be supported, are formed.

In the bottom end portion of the body portion 2, a channel head 7 isprovided. A partition wall 8 divides the inside of the channel head 7into an inlet chamber 71 and an outlet chamber 72. One of ends of eachheat exchanger tube 5 is connected to the inlet chamber 71 and the otherend of each heat exchanger tube 5 is connected to the outlet chamber 72.The inlet chamber 71 has an inlet nozzle 711 communicating with theoutside of the body portion 2. The outlet chamber 72 has an outletnozzle 721 communicating with the outside of the body portion 2. Acooling water pipe (not shown in the drawing) through which the primarycooling water is supplied from the pressurized water reactor isconnected to the inlet nozzle 711. A cooling water pipe (not shown inthe drawing) through which the primary cooling water, after exchangingheat, is supplied to the pressurized water reactor is connected to theoutlet nozzle 721.

Provided in the upper half portion of the body portion 2 are asteam-water separator 9 which separates the steam flow into steam andhot water and a moisture separator 10 which removes moisture from theseparated steam to provide a steam condition close to the dry steam.Between the steam-water separator 9 and the heat exchange tube bundle51, a water supply tube for a steam generator for supplying a secondarycooling water into the body portion 2 from outside (hereinafter simplyreferred to as a “water supply tube”) 20 is inserted. A steam dischargeport 12 is formed on the top end portion of the body portion 2. Providedin the lower half portion of the body portion 2 is a water supplypassage 13 which allows the secondary cooling water supplied from thewater supply tube 20 into the body portion 2 to fall through the gapbetween the body portion 2 and the tube bundle shroud 3, make turn atthe tube plate 4, and ascend along the heat exchange tube bundle 51.Note that, a steam supply passage (not shown in the drawing) forsupplying steam to the turbine is connected to the steam discharge port12. A cooling water pipe (not shown in the drawing) for supplying thesecondary cooling water recovered in a steam condenser (not shown in thedrawing), by cooling the steam used in the turbine, is connected to thewater supply tube 20.

In the steam generator 1 as described above, the primary cooling waterheated in the pressurized water reactor is transferred to the inletchamber 71 and finally to the outlet chamber 72 by passing through alarge number of heat exchange tubes 5. Further, the secondary coolingwater cooled by the steam condenser is transferred to the water supplytube 20, and then supplied into the body portion 2 via the water supplytube 20. In the embodiment, the secondary cooling water may be simplyreferred to as “cooling water.” The cooling water supplied to the bodyportion 2 ascends along the heat exchange tube bundle 51, passingthrough the water supply passage 13. In this step, heat is exchangedbetween the high-pressure and high-temperature primary cooling water andthe secondary cooling water. Then, the cooled primary cooling waterreturns to the pressurized water reactor through the outlet chamber 72.Further, the secondary cooling water which exchanged heat with thehigh-pressure and high-temperature primary cooling water ascends in thebody portion 2 and is separated into steam and hot water in thesteam-water separator 9. Then, the moisture is removed in the moistureseparator 10 and the separated steam is transferred to the turbine.

The water supply tube 20 includes a tubular passage in which the coolingwater supplied from outside the steam generator 1 flows and an effluencetube 25 which allows effluence of the cooling water in the tubularpassage to a space 40 in the steam generator 1 (see FIG. 2 to FIG. 4).The water supply tube 20 is arranged so as to allow effluence of thecooling water below the water level of the cooling water in the space 40during the operation of the steam generator 1. When supplying of thecooling water from outside the steam generator 1 stops or starts, suchas in a shutdown and a startup of a nuclear reactor plant, thermalstratification may occur in the water supply tube 20. For example, whena cooling water with low temperature is supplied, with a small flowrate, to the water supply tube 20 containing high-temperature coolingwater or steam, thermal stratification between the cooling water withlow temperature and the cooling water with high temperature may occurinside the tube, or thermal stratification between steam and coolingwater may occur. When thermal stratification is generated in the tube,stress causing fatigue is generated, which is not preferable. It ispreferable if thermal stratification in the water supply tube 20 can besuppressed. Particularly, it is preferable if thermal stratification canbe suppressed in the portion of the water supply tube 20 which isinserted in a penetration hole penetrating the body portion 2.

In the steam generator 1, as will be described referring to FIG. 2 toFIG. 4, a generator internal tube portion 22 of the water supply tube 20of the embodiment is arranged inside the steam generator 1 and includesa connection tube portion 24 (e.g., see FIG. 2) bent to raise thedownstream side from the insert tube portion 21 inserted in thepenetration hole 112 penetrating the body portion 2 and a tilted tubeportion 233 (e.g., see FIG. 2) bent to lower the further downstreamside. Since the bent portion is provided to raise the downstream side,along the flow direction of the cooling water supplied from outside,from the insert tube portion 21, the cooling water passes through theinsert tube portion 21 within a short period of time before developingthermal stratification so that generation of thermal stress in the bodyportion 2 is suppressed. Further, since the water supply tube 20 whichis first bent to raise the downstream side is then bent to lower thefurther downstream side, the degree of freedom of water supply tube 20in designing arrangement regarding other structures in the steamgenerator 1 and the degree of freedom in designing elevation of thewater level in the generator are provided.

As illustrated in FIG. 2, the water supply tube 20 includes the inserttube portion 21 and the generator internal tube portion 22. Both theinsert tube portion 21 and the generator internal tube portion 22 aretubular members having a circular cross section. A tubular passage isformed along each axial direction of the insert tube portion 21 and thegenerator internal tube portion 22. The cooling water supplied fromoutside the steam generator 1 flows through the tubular passage of thegenerator internal tube portion 22 via the insert tube portion 21. Theeffluence of the cooling water flowing through the tubular passage ofthe generator internal tube portion 22 from the tubular passage of thegenerator internal tube portion 22 to the space 40 in the steamgenerator 1 via an effluence tube 25, which will be described below, isgenerated.

The body portion 2 includes a nozzle 11. The nozzle 11 includes aprotrusion 111 protruding toward the radially outward direction of thebody portion 2. In the nozzle 11, a penetration hole 112 penetrating thenozzle 11 along the axial direction of the protrusion 111 is formed. Theinsert tube portion 21 engages with the penetration hole 112 from theradially inner side of the body portion 2. The insert tube portion 21 issecured to the nozzle 11 by welding or the like so that the outercircumferential surface of the insert tube portion 21 and the innercircumferential surface of the protrusion 111 face each other. That is,the insert tube portion 21 is inserted in the penetration hole 112penetrating the body portion 2 of the steam generator 1. The centralaxis of the nozzle 11, that is, the central axis of the penetration hole112 is horizontally provided and correspondingly, the insert tubeportion 21 extends in the horizontal direction. Further, the insert tubeportion 21 linearly extends along the radial direction of the bodyportion 2.

The generator internal tube portion 22 is arranged inside the bodyportion 2, that is, inside the steam generator 1. As illustrated in FIG.2 and FIG. 3, the generator internal tube portion 22 includes a ringtube portion 23 extending in a ring shape and a connection tube portion24 branching off from the ring tube portion 23 to connect the ring tubeportion 23 and the insert tube portion 21. The ring tube portion 23extends along the circumferential direction of the body portion 2,routing along the inner wall surface 2 a of the body portion 2illustrated in FIG. 2. For example, the ring tube portion 23 is arrangedon the same axis as the central axis 50 of the body portion 2. Asillustrated in FIG. 2, the ring tube portion 23 is supported on theinner wall surface 2 a of the body portion 2 via a stay 14. The ringtube portion 23 includes a horizontal ring tube portion 231 and an upperring tube portion 232 raised vertically higher than the horizontal ringtube portion 231.

The horizontal ring tube portion 231 extends in the horizontaldirection. As illustrated in FIG. 2, the tubular passage formed in thehorizontal ring tube portion 231 along the axial direction, that is, ahorizontal ring tubular passage 231 a also extends in the horizontaldirection. That is, the top end 231 b in any of cross sections,perpendicular to the flow direction of the cooling water, of thehorizontal ring tubular passage 231 a has the same vertical location.Further, the bottom end 231 c in any of cross sections, perpendicular tothe flow direction of the cooling water, of the horizontal ring tubularpassage 231 a has the same vertical location. In other words, thecentral axis of the horizontal ring tubular passage 231 a extends on thesame horizontal plane and the horizontal ring tubular passage 231 a hasa constant diameter. In the ring tube portion 23, the horizontal ringtube portion 231 in which the horizontal ring tubular passage 231 a isformed is arranged farther than the tilted tube portion 233, along theflow direction of the cooling water, from the insert tube portion 21.That is, the horizontal ring tubular passage 231 a is arranged in thedownstream side, in the flow direction of the cooling water suppliedfrom outside the steam generator 1, than the tubular passage 233 e ofthe tilted tube portion 233.

As illustrated in FIG. 3, the upper ring tube portion 232 includes twotilted tube portions 233 and an upper horizontal tube portion 234. Thetilted tube portion 233 is connected to the insert tube portion 21 viathe upper horizontal tube portion 234 and the connection tube portion24. That is, the tilted tube portion 233 is located with the longerdistance, along the flow direction of the cooling water in the generatorinternal tube portion 22, from the insert tube portion 21 than theconnection tube portion 24. In other words, the distance of the flowpassage from the insert tube portion 21 to the tilted tube portion 233is longer than the distance of the flow passage from the insert tubeportion 21 to the connection tube portion 24.

The upper horizontal tube portion 234 is a linear tube portion extendingin the horizontal direction. The connection tube portion 24 branches offfrom the upper horizontal tube portion 234. The connection tube portion24 branches off from the bottom portion of the upper horizontal tubeportion 234 toward the outer side along the radial direction of the bodyportion 2. The end portion, in the side opposite to the side connectedto the upper horizontal tube portion 234, of the connection tube portion24 is connected to the insert tube portion 21. That is, the connectiontube portion 24 branches off from the ring tube portion 23 to connectthe ring tube portion 23 and the insert tube portion 21. The connectiontube portion 24 is tilted so that the side having the greater distancefrom the insert tube portion 21 along the flow direction of the coolingwater is located vertically higher than the side having the smallerdistance from the insert tube portion 21. That is, the connection tubeportion 24 is tilted so that the end portion 24 b side connected to theupper horizontal tube portion 234 is located vertically higher than theend portion 24 a side connected to the insert tube portion 21.Accordingly, the tubular passage 24 c formed in the connection tubeportion 24 is tilted so that the side having the greater distance fromthe insert tube portion 21 along the flow direction of the cooling wateris located vertically higher than the side having the smaller distancefrom the insert tube portion 21. The tubular passage 24 c formed in theconnection tube portion 24 corresponds to a first tilted portion. As forthe tubular passage 24 c, the gradient of the flow passage is greater ata location with a greater distance from the insert tube portion 21 thana location with a smaller distance from the insert tube portion 21.

The tilted tube portions 233 are formed on respective both sides, in theaxial direction, of the ring tube portion 23 with the connection tubeportion 24 in between. One of tilted tube portions 233 connects one ofends of the upper horizontal tube portion 234 and one of ends of thehorizontal ring tube portion 231. The other of tilted tube portions 233connects the other end of the upper horizontal tube portion 234 and theother end of the horizontal ring tube portion 231. The tilted tubeportion 233 is tilted so that the side having the greater distance fromthe insert tube portion 21 along the flow direction of the cooling wateris located vertically lower than the side having the smaller distancefrom the insert tube portion 21. That is, as illustrated in FIG. 4, thetilted tube portion 233 is tilted so that the side with the end portion233 b connected to the horizontal ring tube portion 231 is locatedvertically lower than the side with the end portion 233 a connected tothe upper horizontal tube portion 234. Accordingly, the tubular passage233 e formed in the tilted tube portion 233 is tilted so that the sidehaving the greater distance from the insert tube portion 21 along theflow direction of the cooling water is located vertically lower than theside having the smaller distance from the insert tube portion 21. Thetubular passage 233 e corresponds to a second tilted portion.

The tilted tube portion 233 of the embodiment includes two elbow parts233 c and 233 d which are connected in serial. One of the elbow parts,that is, 233 c extends toward the vertically higher side from aconnection 233 g between two elbows and is bent toward one of the sidesalong the circumferential direction. The other elbow part, that is, 233d extends toward the vertically lower side from the connection 233 g andis bent toward the other side along the circumferential direction. Inthis manner, the tilted tube portion 233 is bent downward from the upperhorizontal tube portion 234 to be connected to the horizontal ring tubeportion 231. Further, as illustrated in FIG. 2, the tilted tube portion233 is tilted so that the vertically lower side of the tilted tubeportion 233 is located in radially outer side of the body portion 2 thanthe vertically higher side of the tilted tube portion 233. That is, thevertically lower side of the tilted tube portion 233 is closer to theinner wall surface 2 a of the body portion 2 than the vertically higherside of the tilted tube portion 233. Arranged in this manner, even whenany other structure is arranged in the radially inner region of the bodyportion 2, the ring tube portion 23 can be arranged without interferingwith the other structure. Note that, the tilt in the radial direction ofthe tilted tube portion 233 is not limited to the configurationdescribed above. The tilt of the tilted tube portion 233 may suitably bedetermined in any direction as long as the interference between otherstructures and the ring tube portion 23 can be avoided.

Further, since the first tilted portion, which is an upward-bent portionof the tubular passage, is formed in the connection tube portion 24 asthe tubular passage 24 c and the second tilted portion, which is adownward-bent portion of the tubular passage, is formed in the ring tubeportion 23 as the tubular passage 233 e, a large degree of freedom isprovided to the arrangement of the upward-bent portion and thedownward-bent portion of the tubular passage. In the generator internaltube portion 22 of the embodiment, the ring tube portion 23 is formed inthe circumferential direction, branching from both sides of theconnection tube portion 24. If both the first tilted portion, which isthe upward-bent portion, and the second tilted portion, which is thedownward-bent portion, are to be formed in the connection tube portion24, that is, at a location upstream of the location from which the ringtube portion 23 branches, a large space is necessary. If both the firsttilted portion and the second tilted portion are to be formed in theconnection tube portion 24, the connection tube portion 24 needs to bebent in a U-shape or a V-shape, resulting in the connection tube portion24 greatly protruding along the radial direction toward the center ofthe body portion 2. As a result, the connection tube portion 24 islikely to interfere with other structures.

Contrarily, by forming the tubular passage 233 e as the second tiltedportion in the ring tube portion 23 branching from the connection tubeportion 24, the space for forming the second tilted portion is easilyprovided. According to the technique of forming the second tiltedportion (tubular passage 233 e) by tilting the portion of the ring tubeportion 23 as in the embodiment, the second tilted portion can extendalong the circumferential direction. That is, the second tilted portioncan be formed avoiding interference with the structure arranged in thecentral side along the radial direction of the body portion 2.Therefore, the degree of freedom of arranging the second tilted portionis large. For example, as described above, the interference with otherstructures can be avoided by providing a tilt to the tilted tube portion233 so that the vertically lower side of the tilted tube portion 233 isarranged in the radially outer side of the body portion 2 than thevertically higher side of the tilted tube portion 233.

A constant tube diameter (inner diameter) can be provided for each ofthe insert tube portion 21, the connection tube portion 24, and the ringtube portion 23. In the embodiment, tube diameters of the insert tubeportion 21 and the connection tube portion 24 are the same, and the tubediameter of the ring tube portion 23 is smaller than the tube diameterof the connection tube portion 24.

The ring tube portion 23 includes an effluence tube 25. The effluencetube 25 functions as an effluence unit to allow effluence of coolingwater, in the tubular passage formed in the ring tube portion 23, fromthe tubular passage to the space 40 in the steam generator 1. Theeffluence tube 25 is a hollow cylindrical member. A plurality ofeffluence tubes 25 is arranged on the ring tube portion 23 along theextending direction of the ring tube portion 23. As illustrated in FIG.4, a plurality of penetration holes 25 a, penetrating the cylindricalportion of the effluence tube 25 in the radial direction, is provided inthe cylindrical portion of the effluence tube 25. Further, one of endsof the effluence tube 25 in the axial direction is connected to thetubular passage of the ring tube portion 23 via a flow hole, which isnot illustrated in the drawing, formed in the ring tube portion 23. Theflow hole is formed in the top portion of the ring tube portion 23. Thatis, the effluence tube 25 is connected to the upper end of the tubularpassage, when viewed from the axial direction of the tubular passage,formed in the ring tube portion 23. The end portion in the verticallyhigher side of the effluence tube 25, that is, the end portion in theopposite side to the end portion connected to the ring tube portion 23is closed.

When the cooling water is supplied to the ring tube portion 23 via theinsert tube portion 21 from outside the steam generator 1, the coolingwater flows into the effluence tube 25 from the tubular passage of thering tube portion 23, and then effluence of the cooling water into thespace 40 in the steam generator 1 is generated via the penetration hole25 a. A large number of penetration holes 25 a are uniformly arranged inthe circumferential direction and the axial direction in the effluencetube 25. Therefore, uniform effluence of the cooling water is generatedaround the effluence tube 25. Note that, the effluence tube 25 is notprovided on the connection tube portion 24, that is, the section, inwhich the first tilted portion is formed, in the generator internal tubeportion 22.

Since the flow hole communicating between the tubular passage of thering tube portion 23 and the effluence tube 25 are formed on the ridgeof the ring tube portion 23, the decrease in the water level of thecooling water in the tubular passage of the ring tube portion 23 issuppressed, even when the water level of the cooling water in the steamgenerator 1 is low enough to expose the ring tube portion 23 above thewater level. In this manner, the generation of a steam-pocket in thetubular passage of the ring tube portion 23 is suppressed.

Further, in the water supply tube 20 of the embodiment, the bottom end234 b of the cross section of the tubular passage 234 a formed in theupper horizontal tube portion 234 is located vertically higher than thetop end 21 a of the inner wall surface of the insert tube portion 21. Inthis manner, the generation of thermal stratification in the insert tubeportion 21 is suppressed as will be described below.

As illustrated in FIG. 2, the bottom end 234 b of the cross section,perpendicular to the flow direction of the cooling water, of the tubularpassage 234 a formed in the upper horizontal tube portion 234 is locatedvertically higher than the top end 21 a of the inner wall surface of theinsert tube portion 21 at the connection between the insert tube portion21 and the connection tube portion 24. In other words, the crosssection, perpendicular to the flow direction of the cooling water, ofthe tubular passage 234 a does not intersect with a horizontal plane 30including the top end 21 a of the inner wall surface of the insert tubeportion 21 at the connection between the insert tube portion 21 and theconnection tube portion 24. At the same time, the bottom end 234 b ofthe cross section is located vertically higher than the horizontal plane30. In this manner, even when the water level of the cooling water inthe steam generator 1 decreases, the decrease in the water level in thetube, which is in the insert tube portion 21 side from the upperhorizontal tube portion 234, of the water supply tube 20 can besuppressed. Specifically, the decrease in the water level of the coolingwater is suppressed so that the water level will not to be lower thanthe bottom end 234 b of the tubular passage 234 a, thereby keeping theinsert tube portion 21 filled with the cooling water. As a result, inthe insert tube portion 21, the generation of the steam-pocket in thetube is suppressed, thereby suppressing generation of thermalstratification in the insert tube portion 21. Particularly, theconnection tube portion 24 of the embodiment does not include theeffluence tube 25. Therefore, the decrease in the water level of thecooling water is surely suppressed so that the water level will not belower than the bottom end 234 b of the tubular passage 234 a.

Different from the water supply tube 20 of the embodiment, a certainperiod of time is necessary for the whole water supply tube to be filledwith the cooling water after start supplying cooling water to the watersupply tube containing a low level of water as in the start of theoperation of steam generator 1. Such is the case for a water supply tubewhich includes the insert tube portion 21 and the ring tube portion 23horizontally extending in the same height and does not have anupward-bent portion like the connection tube portion 24 or adownward-bent portion like the tilted tube portion 233. Until the waterlevel in the water supply tube rises to the enough level, layers ofsteam and cooling water separately exist in the insert tube portion 21,with the generated stress remaining in the insert tube portion 21causing fatigue. Further, a water hammer may occur by the steam makingcontact with the cooling water. It is desirable to suppress thesethermal stress and water hammer in the vicinity of the nozzle 11provided as a boundary.

According to the water supply tube 20 of the embodiment, when supplyingof the cooling water to the water supply tube 20 containing a low levelof water starts, first, the insert tube portion 21 is filled with thecooling water, and then after the rise in the water level, the coolingwater is supplied from the connection tube portion 24 to the horizontalring tube portion 231 via the upper ring tube portion 232. In thismanner, the period of time in which the steam layer and the coolingwater layer are generated in the insert tube portion 21 can beshortened, thereby suppressing generation of stress causing fatigue inthe insert tube portion 21.

Further, according to the water supply tube 20 of the embodiment, thestate in which layers of cooling water having different temperaturesexist separately in the insert tube portion 21 can easily be avoided, aswill be described below.

For example, when low-temperature cooling water is supplied, with asmall flow rate, from outside the steam generator 1 into the watersupply tube 20 with high-temperature cooling water remaining therein, orwhen high-temperature cooling water flows into the water supply tube 20from the space 40 outside the water supply tube 20, thermalstratification is generated in which layers of low-temperature coolingwater and high-temperature cooling water separately exist. The thermalstratification thus generated is likely to remain longer in the inserttube portion 21 of the water supply tube including the insert tubeportion 21 and the ring tube portion 23 horizontally extending in thesame height.

According to the water supply tube 20 of the embodiment, whenlow-temperature cooling water is supplied, with a small flow rate, fromoutside the steam generator 1 into the water supply tube 20 withhigh-temperature cooling water remaining therein, the insert tubeportion 21 is rapidly filled with the cooling water supplied fromoutside, generating the effluence of the high-temperature cooling waterin the insert tube portion 21 from the connection tube portion 24 to theupper ring tube portion 232 and the horizontal ring tube portion 231. Inthis manner, the water supply tube 20 according to the embodimenteliminates the thermal stratification in the insert tube portion 21 in ashort period of time compared to the supply tube including the inserttube portion 21 and the ring tube portion 23 horizontally extending inthe same height.

In the embodiment, the tubular passage 234 a formed in the upperhorizontal tube portion 234 corresponds to the tubular passage betweenthe first tilted portion and the second tilted portion. Further, in theembodiment, the bottom end 234 b of the cross section, perpendicular tothe flow direction of the cooling water, of the entire section of thetubular passage 234 a is arranged vertically higher than the horizontalplane 30. However, the present invention is not limited to theconfiguration. Any configuration is allowed as long as the bottom end234 b of the cross section, perpendicular to the flow direction of thecooling water, of the tubular passage 234 a is arranged verticallyhigher than the horizontal plane 30 in at least a portion of thesection, along the flow direction, of the tubular passage 234 a.

As a water supply tube capable of suppressing thermal stratification inthe insert tube portion 21, a water supply tube 120 formed such that thewhole ring tube portion 123 is raised than the insert tube portion 21 asillustrated in FIG. 5 and FIG. 6 can be used. FIG. 5 is a crosssectional view illustrating an example of the water supply tube capableof suppressing thermal stratification in an insert tube portion. FIG. 6is a perspective view illustrating an example of the water supply tubecapable of suppressing thermal stratification in an insert tube portion.The ring tube portion 123 of the water supply tube 120 does not includethe tilted tube portion 233 as in the embodiment. As illustrated in FIG.5, in the tubular passage 123 a formed in the ring tube portion 123, thevertical location of the top end 123 b of the cross sectionperpendicular to the flow direction of the cooling water is the same atany location in the flow direction of the cooling water. That is, at anylocation in the flow direction of the cooling water, the top end 123 bof the cross section, perpendicular to the flow direction of the coolingwater, of the tubular passage 123 a is on the same horizontal plane.

As illustrated in FIG. 6, the ring tube portion 123 includes a taperedportion 123 c. The tapered portion 123 c is formed in the vicinity ofthe connection between the ring tube portion 123 and the connection tubeportion 124. The tapered portion 123 c is formed on both sides, in thecircumferential direction, of the connection between the ring tubeportion 123 and the connection tube portion 124. The tapered portion 123c has a tapered shape in which the diameter is smaller for a locationfarther from the connection tube portion 124 along the flow direction ofthe cooling water in the ring tube portion 123. In the tapered portion123 c, the flow area of the tubular passage 123 a gradually decreases asthe cross section is distanced from the connection tube portion 124. Inthe ring tube portion 123, in accordance with both ends of the taperedportion 123 c having different diameters, the diameter of the ring-sideconnection tube portion 123 d, which is arranged closer to theconnection tube portion 124 than the tapered portion 123 c, is largerthan the diameter of the portion 123 e which is arranged farther fromthe connection tube portion 124 than the tapered portion 123 c. Theconnection tube portion 124 is similar to the connection tube portion 24of the water supply tube 20 and is tilted so that the side having thegreater distance from the insert tube portion 21 along the flowdirection of the cooling water is located vertically higher than theside having the smaller distance from the insert tube portion 21.

The ring-side connection tube portion 123 d is a linear tubular portionhaving a constant diameter. As illustrated in FIG. 5, the bottom end 123f of the cross section, perpendicular to the flow direction of thecooling water, of the ring-side connection tube portion 123 d is locatedvertically higher than the top end 21 a of the inner wall surface of theinsert tube portion 21 at the connection between the insert tube portion21 and the connection tube portion 124.

The water supply tube 120 can also suppress the generation of thermalstratification in the insert tube portion 21 or rapidly eliminate thethermal stratification, thereby suppressing generation of thermal stresscausing fatigue. However, when the whole ring tube portion 123 is raisedagainst the insert tube portion 21, the ring tube portion 123 is easilyexposed to a gas layer when the water level in the steam generator 1decreases.

Contrarily, as illustrated in FIG. 3 and FIG. 4, in the water supplytube 20 of the embodiment, the generator internal tube portion 22 isbent to raise itself against the insert tube portion 21 at theconnection tube portion 24, and then bent to lower itself at the tiltedtube portion 233. In this manner, the vertical location of thehorizontal ring tube portion 231 is lowered, thereby suppressingexposure of the horizontal ring tube portion 231 above the surface ofthe cooling water. As illustrated in FIG. 2, the top end 231 b of thecross section, perpendicular to the flow direction of the cooling water,of the tubular passage 231 a in the horizontal ring tube portion 231 islocated vertically lower than the horizontal plane 30 including the topend 21 a of the inner wall surface of the insert tube portion 21 at theconnection between the insert tube portion 21 and the connection tubeportion 24. Configured in this manner, the tubular passage 231 a in thehorizontal ring tube portion 231 is kept below the water level even whenthe cooling water level in the steam generator 1 is low enough to startexposing the insert tube portion 21. By lowering chances of thehorizontal ring tube portion 231 exposed above the cooling water, thegeneration of a steam-pocket in the tubular passage 231 a can besuppressed.

The vertical location of the tubular passage 231 a formed in thehorizontal ring tube portion 231 is not limited to the configurationdescribed above. Any vertical location can be determined. For example,in the embodiment, the top end 231 b of the cross section, perpendicularto the flow direction of the cooling water, of the tubular passage 231 ais located vertically lower than the central axis X of the insert tubeportion 21. Configured in such manner, in the water supply tube 20 ofthe embodiment, any vertical location of the tubular passage 231 a inthe horizontal ring tube portion 231 can be determined, maintaining theeffect of suppressing thermal stratification in the insert tube portion21.

Further, in the embodiment, the upper horizontal tube portion 234 isprovided with an effluence tube 251 (25). This configuration suppressessuction of the cooling water in the insert tube portion 21 out into thehorizontal ring tube portion 231 side when the cooling water level inthe steam generator 1 decreases. For example, in a configuration withoutthe effluence tube 251 provided on the upper horizontal tube portion234, when the cooling water level is low enough to start exposing thehorizontal ring tube portion 231, and when the supply of the coolingwater from outside to the water supply tube 20 is stopped, the coolingwater in the insert tube portion 21 located higher than the horizontalring tube portion 231 may be suctioned out into the horizontal ring tubeportion 231 side. In the embodiment, the effluence tube 251 provided onthe upper horizontal tube portion 234 is exposed when the cooling waterlevel in the steam generator 1 decreases, thereby opening the tubularpassage 234 a. In this manner, the suction of the cooling water in theinsert tube portion 21 out into the horizontal ring tube portion 231 issuppressed.

Note that, the vertical location of the horizontal ring tube portion 231can be determined based on the predetermined target for controlling thewater level of the cooling water in the space 40 in the steam generator1. The target water level of the cooling water is determined dependingon a control parameter of a nuclear plant including the steam generator1. For example, when a lower limit is determined for the target of thewater level to be controlled, it may be configured that the top end 231b of the cross section, perpendicular to the flow direction of thecooling water, of the tubular passage 231 a is located vertically lowerthan the lower limit of the water level. Configured in this manner, aslong as the cooling water level in the steam generator 1 is at, orhigher than, the lower limit of the target water level, the tubularpassage 231 a is kept below the surface of the cooling water. Thereby,the generation of a steam-pocket in the tubular passage 231 a issuppressed.

Further, the vertical location of the horizontal ring tube portion 231may be determined so that, for example, the tubular passage 231 a in thehorizontal ring tube portion 231 is located below the cooling waterlevel in the space 40 in the steam generator 1 even when a supplied flowrate of low-temperature cooling water is small, as in the start-up orshutdown under a hot state in a plant.

In the embodiment, the tube portion including the effluence tube 25 isprovided as the ring tube portion 23 extending in a ring shape. However,the shape of the tube portion including the effluence tube 25 is notlimited to such configuration.

REFERENCE SIGNS LIST

-   -   1 steam generator    -   2 body portion    -   11 nozzle    -   112 penetration hole    -   20 water supply tube    -   21 insert tube portion    -   22 generator internal tube portion    -   23 ring tube portion    -   231 horizontal ring tube portion    -   232 upper ring tube portion    -   233 tilted tube portion    -   234 upper horizontal tube portion    -   24 connection tube portion    -   25 effluence tube    -   30 horizontal plane

1. A water supply tube for a steam generator comprising: an insert tubeportion horizontally extending and configured to be inserted in apenetration hole penetrating a shell member of the steam generator; anda generator internal tube portion connected to the insert tube portionand arranged inside the steam generator, wherein the generator internaltube portion includes a tubular passage formed in an axial direction ofthe generator internal tube portion and an effluence unit allowingeffluence of cooling water in the tubular passage from the tubularpassage to a space in the steam generator, the tubular passage allowingcooling water supplied from outside the steam generator via the inserttube portion to flow in the tubular passage, wherein the tubular passageincludes a first tilted portion which is tilted so that a side having agreater distance from the insert tube portion along a flow direction ofcooling water is located vertically higher than a side having a smallerdistance from the insert tube portion and a second tilted portion whichis located with a greater distance from the insert tube portion alongthe flow direction than the first tilted portion and is tilted so that aside having a greater distance from the insert tube portion along theflow direction is located vertically lower than a side having a smallerdistance from the insert tube portion, and wherein, in at least aportion of a section, along the flow direction, of the tubular passagebetween the first tilted portion and the second tilted portion, a bottomend of a cross section, perpendicular to the flow direction, of thetubular passage is arranged vertically higher than a horizontal planeincluding a top end of an inner wall surface of the insert tube portionat a connection between the insert tube portion and the generatorinternal tube portion.
 2. The water supply tube for a steam generatoraccording to claim 1, wherein the effluence unit is not included in asection, of the generator internal tube portion, in which the firsttilted portion is formed.
 3. The water supply tube for a steam generatoraccording to claim 1, wherein the generator internal tube portionincludes a ring tube portion extending in a ring shape along an innercircumferential surface of the shell member and a connection tubeportion branching off from the ring tube portion to connect the ringtube portion and the insert tube portion, wherein the first tiltedportion is provided as the tubular passage formed in the connection tubeportion, and wherein the second tilted portion is provided as thetubular passage formed in the ring tube portion, the second tiltedportion being formed on each of both ends, in an axial direction, of thering tube portion with the connection tube portion in between.
 4. Thewater supply tube for a steam generator according to claim 3, wherein ahorizontal ring tubular passage which is the tubular passage extendingin a horizontal direction is formed in a portion, arranged farther thanthe second tilted portion from the insert tube portion along the flowdirection, of the ring tube portion, and wherein a top end of a crosssection, perpendicular to the flow direction, of the horizontal ringtubular passage is provided vertically lower than the horizontal planeincluding the top end of the inner wall surface of the insert tubeportion at the connection between the insert tube portion and thegenerator internal tube portion.
 5. The water supply tube for a steamgenerator according to claim 3, wherein a horizontal ring tubularpassage which is the tubular passage extending in a horizontal directionis formed in a portion, arranged farther than the second tilted portionfrom the insert tube portion along the flow direction, of the ring tubeportion, and wherein a top end of a cross section, perpendicular to theflow direction, of the horizontal ring tubular passage is arrangedvertically lower than a lower limit of a target for controlling a waterlevel of cooling water in the space in the steam generator.